Spin-on formulation and method for stripping an ion implanted photoresist

ABSTRACT

A spin-on formulation that is useful in stripping an ion implanted photoresist is provided that includes an aqueous solution of a water soluble polymer containing at least one acidic functional group, and at least one lanthanide metal-containing oxidant. The spin-on formulation is applied to an ion implanted photoresist and baked to form a modified photoresist. The modified photoresist is soluble in aqueous, acid or organic solvents. As such one of the aforementioned solvents can be used to completely strip the ion implanted photoresist as well as any photoresist residue that may be present. A rinse step can follow the stripping of the modified photoresist.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/643,454, filed Dec. 21, 2009 the entire content and disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The present invention relates to semiconductor device manufacturing and,more particularly, to the removal or stripping of an ion implantedphotoresist material and related photoresist material residue from asurface of a semiconductor structure during processing thereof.

The fabrication of integrated circuits (ICs) on a semiconductorsubstrate typically includes the use of a front-end-of-the line (FEOL)process which forms one or more semiconductor devices such as, forexample, transistors, on a surface of the semiconductor substrate. In atypical FEOL process, various selected areas of the semiconductorsubstrate are exposed to ion implantation of impurities (e.g., dopants)such as, for example, phosphorus, boron or arsenic, in order to createp-type and/or n-type regions. The doping of the selected areas of thesubstrate begins with the deposition of a photoresist layer. Thephotoresist layer is typically dried and cured after deposition. Thephotoresist is photoactive, and can be modified by exposure to selectedforms of radiant energy. Exposure of the photoresist is performed in aphotolithography step where the substrate is exposed to radiant energyof selected wavelengths through a mask. This mask defines those areas ofthe photoresist-coated substrate, which are subjected to the radiationand those that are not. Typically, the areas of photoresist that aresubject to the radiation are modified and can be removed by developing.This method of pattern transfer (from mask to substrate) leavesphotoresist covering those areas of the substrate that were shielded bythe mask.

Ion implantation is then employed to drive the impurity dopants intothose areas of the substrate that are not protected by the photoresist.Subsequent to this step, all the photoresist must be removed before thesubstrates are annealed, oxidized or processed in diffusion furnaces.Currently, post-implant photoresist removal is performed by wet etching,dry etching or a combination of wet etching and dry etching. Wet etchingprocesses typically involve the employment of a mixture of sulfuric acidand hydrogen peroxide to remove the resist and other organiccontaminants that might be present. The photoresist can also be removedusing dry etching processes, typically involving the use of plasmaoxidation. In a plasma process, a source of oxidant, such as oxygen, isintroduced into a plasma field excited either by radio frequency ormicrowave frequency energy.

The recent process trends in the manufacture of IC's have caused anincrease in the level of doping. This has been achieved by increasingthe energy and density of the ion flux directed at the substrate duringthe ion implantation process. As a consequence, the surface of thephotoresist that shields certain areas of the substrate from the ionimplantation process is itself modified. Due to the high energy and fluxdensity, surface layers of the photoresist undergo chemical and physicalmodification. The higher temperatures resulting from the ion bombardmentcause further baking and hardening of the top surface layer of thephotoresist. Also, the ion flux causes implantation of the resist withthe dopant atoms. Moreover, the photoresist undergoes significantcross-linking and becomes more resistant to post-implant removalprocesses. The modified surface layer of the ion implanted photoresistis typically referred to in the art as a crusted surface layer.

The conventional techniques of removing the ion implanted photoresisthaving the crusted surface layer also involve a combination of dry andwet etching, or a wet etch using sulfuric-acid-based chemistries,typically a mixture of sulfuric acid and hydrogen peroxide. A commondrawback of all prior art strip methodologies includes the incompleteremoval of the crusted photoresist present on the substrate surface postion implantation.

Moreover, resist removal via conventional techniques has been shown toprocess excessive semiconductor material, e.g., Si, from the structureas well as dopant loss and possible damage to fragile semiconductorstructures. Also, when metal gates are present on the surface of thesubstrate during the ion implantation process, the prior art resiststripping methods mentioned above would damage the metal gate byoxidizing the same.

SUMMARY OF THE INVENTION

In an embodiment of the invention, a polymeric layer containing anoxidant is formed on a photoresist material post ion implantation. Thepolymeric layer is formed from an aqueous spin-on formulation thatincludes a water soluble polymer containing at least one acidicfunctional group, and at least one lanthanide metal-containing oxidant.A bake step is employed which causes a reaction between the polymericlayer and the ion implanted photoresist so that crusted portions of theion implanted photoresist as well as the cross-linked regions of the ionimplanted photoresist are made soluble in an aqueous, acidic or organicsolvent. A resist stripping step in an aqueous, acidic or organicsolvent is employed to completely remove the ion implanted photoresistand any resist residue from the structure. A final clean step canoptionally be performed. The aforementioned processing steps can be usedin any semiconductor device fabrication process and at anytime of thefabrication process. For example, the above processing can be performedon a bare semiconductor substrate or on a semiconductor substrate thathas been processed to include at least one gate stack.

In some embodiments of the invention in which a metal gate material,such as TiN, is present, the above processing can be employed withoutdamaging the metal gate material. That is, the above processing can beemployed without removing any significant portion of the metal gatematerial in contrast to commonly used strip technology such as a wetetch using sulfuric acid and hydrogen peroxide, which severely attacksthe metal gate material.

In one aspect, a method of removing a photoresist material post ionimplantation from a surface of a semiconductor structure is provided.The method includes providing a patterned photoresist on a surface of asemiconductor structure. The patterned photoresist has at least oneopening therein that exposes an upper surface of a semiconductorsubstrate of the semiconductor structure. Dopant ions are introducedinto the exposed upper surface of the semiconductor substrate as well asthe patterned photoresist. A thin polymeric film containing an oxidantis formed on at least the exposed upper surfaces of the now ionimplanted and patterned photoresist. A bake step is employed whichcauses a reaction between the thin polymeric film and the ion implantedand patterned photoresist. The reaction forms a modified patternedphotoresist that is soluble in aqueous, acid or organic solvents. Themodified patterned photoresist is removed from the semiconductorstructure by stripping in an aqueous, acid or organic solvent. In someembodiments, a clean step is performed after the modified patternedphotoresist has been removed from the structure.

In another aspect of the invention, a spin-on formulation is providedwhich can be processed into a polymeric film including an oxidant. Inthis aspect of the invention, the spin-on formulation includes anaqueous solution of a water soluble polymer containing at least oneacidic functional group, and at least one lanthanide metal-containingoxidant.

In one embodiment of the invention, the aqueous solution comprisespolystyrene sulfonic acid as the water soluble polymer containing atleast one acidic functional group, and cerium ammonium nitrate as the atleast one lanthanide metal-containing oxidant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross sectional view)illustrating an initial structure including a patterned photoresisthaving at least one opening therein that exposes an upper surface of asemiconductor substrate of the initial structure that can be employed inone embodiment of the invention.

FIG. 2 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 1 after ion implantation in whichdopants are introduced into the exposed upper surface of thesemiconductor substrate and the patterned photoresist.

FIG. 3 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 2 after forming a polymeric filmcontaining an oxidant on exposed surfaces of at least the ion implantedand patterned photoresist.

FIG. 4 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 3 after baking the ion implanted andpatterned photoresist containing the thin polymeric film thereon.

FIG. 5 is a pictorial representation (through a cross sectional)illustrating the structure of FIG. 4 after resist stripping.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which in one embodiment provides a spin-onformulation and a method of stripping an ion implanted and patternedphotoresist from a semiconductor structure, will now be described ingreater detail by referring to the following discussion and drawingsthat accompany the present application. It is observed that the drawingsof the present application are provided for illustrative proposes and,as such, the drawings are not drawn to scale.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide an understanding ofsome aspects of the present invention. However, it will be appreciatedby one of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “beneath” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

As stated above, a spin-on formulation that is useful in stripping anion implanted and patterned photoresist from a semiconductor structureis provided. The spin-on formulation includes an aqueous solution of awater soluble polymer containing at least one acidic functional group,and at least one lanthanide metal-containing oxidant. The spin-onformulation is applied to an ion implanted and patterned photoresist andbaked to form a modified patterned photoresist that contains the ionimplanted dopants. The modified patterned photoresist is soluble inaqueous, acid or organic solvents. As such one of the aforementionedsolvents can be used to completely strip the modified patternedphotoresist as well as any photoresist residue that may be present. Acleaning, e.g., rinsing, step can follow the stripping of the modifiedpatterned photoresist.

Reference is now made to FIGS. 1-5 which depict various stages ofsemiconductor fabrication before and after ion implantation andstripping operations in accordance with an embodiment of the invention.FIG. 1 illustrates an initial semiconductor structure 10 that can beemployed in one embodiment of the invention. The initial semiconductorstructure 10 includes at least a patterned photoresist 14 having atleast one opening 16 therein that is located atop a semiconductorsubstrate 12. As shown, the at least one opening 16 of the patternedphotoresist 14 exposes a portion of the semiconductor substrate 12 in anarea in which one or more dopants are to be subsequently introduced viaion implantation.

The semiconductor substrate 12 can be a bare semiconductor material or asemiconductor material that is processed to include various isolationregions and/or semiconductor devices, such as metal gates, on thesurface of the semiconductor substrate. The isolation regions and/orsemiconductor devices can be formed utilizing FEOL processing techniquesthat are well known to those skilled in the art. The semiconductorsubstrate 12 includes any semiconductor material including, but notlimited to Si, SiGe, SiGeC, SiC, Ge alloys, GaAs, InAs, InP and otherIII/V or II/Vi compound semiconductors. In addition to these listedtypes of semiconductor materials, the substrate 12 can also be a layeredsemiconductor such as, for example, Si/SiGe, Si/SiC,silicon-on-insulators (SOIs) or silicon germanium-on-insulators (SGOIs).In some embodiments, the semiconductor substrate 12 is a Si-containingsemiconductor material, i.e., a semiconductor material that includessilicon. The semiconductor substrate 12 may include a single crystalorientation or it may include at least two coplanar surface regions thathave different crystal orientations (the latter substrate is referred toin the art as a hybrid substrate).

In one embodiment (not shown), a metal gate stack including at least agate dielectric and a metal gate are formed on the surface of thesemiconductor substrate 12. When such an embodiment is employed, thepatterned photoresist 14 typically protects the metal gate stack, whileleaving a portion of the semiconductor substrate 12 at the footprint ofthe metal gate stack exposed. In such an embodiment, the gate dielectricincludes any gate insulating material including for example,semiconductor or metal oxides, nitrides and/or oxynitrides. For example,the gate dielectric may include silicon oxide, silicon nitride, siliconoxynitride, aluminum oxide, titanium oxide, hafnium oxide, zirconiumoxide and multilayered stacks thereof. The metal gate of the metal gatestack includes any conductive metal, metal nitride and/or metalsilicide. In one embodiment of the invention, the metal gate iscomprised of TiN. In some embodiments, a Si-containing gate electrodematerial can be used with the metal gate electrode material or in placethereof.

The patterned photoresist 14 including the at least one opening 16 isformed by first applying a blanket layer of photoresist material to thesurface of the semiconductor substrate 12. The photoresist material mayinclude any conventional photoresist material including a positive-tonephotoresist material or a negative-tone photoresist material. By‘positive-tone” it is meant that the part of the photoresist that isexposed to photolithography will be removed by a conventional developer,while the unexposed part of the photoresist is not removed. By“negative-tone” it is meant that the part of the photoreisist that isexposed to photolithography will not be removed by a conventionaldeveloper, while the unexposed part of the photoresist is removed. Thephotoresists may include photoacid generators, base additives and/orsolvents, each of which is well known to those skilled in the art and,as such, details regarding those components are not fully provided.

The blanket layer of photoresist material is formed on the surface ofthe semiconductor substrate 12 utilizing conventional techniques wellknown to those skilled in the art including, for example, spin-oncoating, dip coating, evaporation, chemical solution deposition, andchemical vapor deposition. After application of the blanket layer ofphotoresist material, the blanket layer of photoresist material istypically dried and cured utilizing processing conditions that are wellknown to those skilled in the art. The photoresist material is thensubjected to conventional photolithography which includes exposing theblanket layer of photoresist material to a desired pattern of radiationand then removing portions of the exposed photoresist material utilizinga conventional developer so as to form the structure such as shown, forexample, in FIG. 1.

Referring now to FIG. 2, there is illustrated the structure of FIG. 1after introducing at least one dopant into the exposed portions of thesemiconductor substrate 12 utilizing the patterned photoresist 14 as anion implantation mask. As is shown in FIG. 2, a dopant region 18 isformed into the exposed portion of the semiconductor substrate 12. Theion energy or intensity of the ion bombardment determines the depth orthickness of the dopant region 18. The density of the ion fluxdetermines the extent of the doping.

In addition, dopants are also introduced into the patterned photoresistforming an ion implanted and patterned photoresist 14′ which includes acrusted surface layer 15. The crusted surface layer 15 may be comprisedof carbonized and highly crosslinked polymer chains. The crusted surfacelayer 15 is typically depleted of hydrogen and impregnated with theimplant species. The crusted surface layer 15 is denser than theremaining portion 13, e.g., bulk portion, of the ion implanted andpatterned photoresist 14′. The relative density of the crusted surfacelayer 15 depends on the ion flux, while the thickness of the crustedsurface layer 15 depends on the ion energy.

The implantation of dopants described above can be performed by plasmaimmersion ion implantation or by ion beam ion implantation. The types ofdopants that are implanted may vary and include species from Group VA ofthe Periodic Table of Elements, i.e., one of P, As, and Sb, or speciesfrom Group IIIA of the Periodic Table of Elements, i.e., one of B, Al,Ga, and In. In one embodiment of the invention, the dopants include atleast one of B, P and As. The dosage of dopants being implanted mayvary, but typically the dosage of the dopants being implanted is greaterthan 1E15 atoms/cm². The energy of the implant may also vary, with anenergy from 1 keV up to 50 keV being typically employed in oneembodiment of the invention.

It is noted that during this step, small amounts of a material may besputtered to the patterned photoresist sidewalls. This sputteredmaterial may include some of the implant species, other material in theplasma or ion beam, and by-products of the implantation. The actualspecies present within the sputtered material depends on the compositionof the substrate 12 before ion implantation, the photoresist and theimplanted species.

It is also noted that the crusted surface layer 15 is more difficult tostrip than the remaining portion 13 of the ion implanted and patternedphotoresist 14′. Removal rates of the crusted surface layer 15 may be50% or 75% slower than the remaining portion 13 of the ion implanted andpatterned photoresist 14′. Moreover, at elevated temperatures (of about150° C.), the remaining portion 13 of the ion implanted and patternedphotoresist 14′ may outgas and expand relative to the crusted surfacelayer 15. The entire photoresist can thus ‘pop’ as the underlyingphotoresist builds up pressure under the crusted surface layer 15. As isknown to those skilled in the art, photoresist popping is a source ofparticles and process defects because the residues are especially hardto clean from the surface of the substrate as well as the surfaces ofthe tools used to process the structure.

Referring now to FIG. 3, there is illustrated the structure of FIG. 2after forming a polymeric film containing an oxidant on at least theexposed upper surface, e.g., the crusted surface layer 15, of the ionimplanted and patterned photoresist 14′. In FIG. 3, reference numeral 20denotes the polymeric film that is formed. The polymeric film 20 whichincludes the oxidant typically has a thickness from 0.1 micron to 10microns, with a thickness from 1 micron 5 microns being more typical.The oxidant of the polymeric film 20 is a lanthanide metal-containingoxidant as described herein below. The polymer component of thepolymeric film 20 is a water-soluble polymer as described herein belowas well.

The polymeric film 20 containing the oxidant is formed from a spin-onformulation that includes an aqueous solution of a water soluble polymercontaining at least one acidic functional group, and at least onelanthanide metal-containing oxidant. The spin-on formulation is appliedto the ion implanted and patterned photoresist 14′ by utilizing anyconventional spin on process. In short, an excess amount of theaforementioned spin-on formulation is placed on the structure shown inFIG. 2, which is then rotated in a spin coater at high speed in order tospread the spin-on formulation by centrifugal force. Rotation iscontinued while the spin-on formulation spins off the edges of thestructure shown in FIG. 2, until the desired thickness of the polymericfilm 20 is achieved. The spin-on formulation used in forming thepolymeric film 20 is typically spun at 750 revolutions per second to3000 revolutions per second for 30 seconds to 120 seconds. Otherrotational speeds and times can also be used in applying the spin-onformulation to the structure shown in FIG. 2.

As stated above, the spin-on formulation employed in forming thepolymeric film 20 including the oxidant is formed from a spin-onformulation that includes an aqueous solution of a water soluble polymercontaining at least one acidic functional group, and at least onelanthanide metal-containing oxidant. In one embodiment, the spin-onformulation comprises from 5 weight % to 50 weight % of a water solublepolymer containing at least one acidic functional group, from 5 weight %to 50 weight % of the at least one lanthanide metal-containing oxidantand the remaining water. In another embodiment of the present invention,the spin-on formulation comprises from 10 weight % to 35 weight % of awater soluble polymer containing at least one acidic functional group,from 15 weight % to 25 weight % of the at least one lanthanidemetal-containing oxidant and the remaining water.

The water soluble polymers employed in the present invention include anypolymer, copolymer or oligomer including at least one acidic functionalgroup (e.g., a carboxylic acid functional group or sulfonic acidfunctional group) that can be dissolved in water. Examples of suitablewater soluble polymers that can be employed in the present inventioninclude, but are not limited to polyacrylic acid, polymethacrylic acid,polymaleic acid, polystyrene sulfonic acid,polytetraflourostyrenesulfonic acid, poly(ethylene-maleic) acid andpolystyrene carboxylic acid.

The at least one lanthanide metal-containing oxidant includes lanthanidemetal nitrates (e.g., ammonium nitrate), chlorates, perchlorates,bromates, perbromates, permanganates (e.g., potassium permanganate),chromates, and dichromates. According to IUPAC terminology, thelanthanide metals include the fifteen elements with atomic numbers57-71, from lanthanum to lutetium. All lanthanide metals are f-blockelements, corresponding to the filling of the 4f electron shell, exceptfor lutetium which is a d-block lanthanoid. In one embodiment of theinvention, the lanthanide metal employed includes cerium (Ce). In yetanother embodiment, a lanthanide metal ammonium nitrate is employed asthe lanthanide metal-containing oxidant. In a further embodiment of theinvention, cerium ammonium nitrate is employed as the at least onelanthanide metal-containing oxidant.

The spin-formulation is made utilizing conventional techniques that arewell known in the art. In one embodiment, the spin-on formulation ismade by adding the at least one lanthanide metal-containing oxidant toan aqueous solution including a water soluble polymer containing atleast one acidic functional group.

Referring now to FIG. 4, there is shown the structure of FIG. 3 afterperforming a baking step. The baking step causes a reaction between thepolymeric film and the ion implanted and patterned photoresist 14′including the crusted surface layer 15 in which a modified patternedphotoresist 14″ is formed. In particular, the resultant modifiedpatterned photoresist 14″ is more soluble in aqueous, acidic or organicsolvents than the corresponding ion implanted and patterned photoresist14′. Film 14″ may be covered with a film formed by the thermalmodification of film 20, hereby labeled as 20′ in FIG. 4. The bakingstep is typically performed at a temperature from 80° C. to 160° C.,with a baking temperature from 100° C. to 140° C. being even moretypical. The baking step can be performed in an inert ambient including,for example, He, Ar, and/or Ne. Alternatively, the baking step can beperformed in vacuum. In some embodiments of the invention, the bake isperformed on a pre-heated hot plate at standard room conditions, e.g.,in air and at room temperature and at room temperature humidity.

Referring now to FIG. 5, there is shown the structure of FIG. 4 afterremoving the modified patterned photoresist 14″ and modified film 20′from the structure. The removal of the modified patterned photoresist14″ and modified film 20′ can be performed by contacting, e.g., rinsing,the structure shown in FIG. 4 with an aqueous solvent, an acidic solventor an organic solvent. The contact can be performed at room temperature(i.e., a temperature from 20° C. to 40° C.) or at an elevatedtemperature of greater than 70° C. The duration of this contact may varyand is not critical to the practice of the present invention. Typically,the duration of this contact is from 5 minutes to 50 minutes, with aduration of this contact from 15 minutes to 25 minutes being moretypical.

In one embodiment, water is employed as the aqueous solvent. When wateris employed, the contacting in water typically occurs at a temperaturefrom 80° C. to 100° C. The duration of contacting in water is typicallyfrom 10 minutes to 30 minutes.

As stated above, acidic solvents and organic solvents can also be used.Examples of acidic solvents that can be used include, but are notlimited to, sulfuric acid, nitric acid, phosphoric acid, methanesulfonicacid, triflouromethanesulfonic acid, acetic acid, triflouroacetic acid.Examples of organic solvents that can be used include, but are notlimited to, tetrahydrofuran (THF), diethyleneglycol diethylene ether,n-methylpyrrolidone (NMP), dimethylformamide (DMF), dioxane or a mixtureof these organic solvents and water.

It is noted that the above processing results in complete removal of theion implanted and patterned photoresist 14″ including the crustedsurface layer 15 from the structure. It is also noted that the removalof the ion implanted and patterned photoresist 14′ occurs without anysignificant loss of the substrate 12 or dopant within dopant region 18.Moreover, and in embodiments, in which metal gates are present, theabove technique does not result in any damage to the metal gates. Thisis evidence by measuring the thickness of the metal gate before andafter removal of the ion implanted photoresist. When using the aboveprocessing techniques, little or no loss of the metal gate is observedsince the thickness of the metal gate before and after the aboveprocessing is substantially the same.

In some embodiments of the invention, the structure shown in FIG. 5 maybe subjected to a cleaning step after stripping the ion implantedphotoresist from the structure. When a cleaning step is employed, one ofthe above mentioned acids may be used. The optional cleaning step may beperformed at room temperature or at an elevated temperature within theranges mentioned above for the photoresist stripping step. The durationof this contact may vary and is not critical to the practice of thepresent invention. Typically, the duration of this contact is from 5minutes to 30 minutes, with a duration of this contact from 10 minutesto 20 minutes being more typical. In one embodiment, the cleaning stepis performed utilizing H₂SO₄. In such an embodiment, the H₂SO₄ contacttypically occurs at room temperature, for a duration from 10 to 30minutes.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A spin-on formulation comprising an aqueous solution of a watersoluble polymer containing at least one acidic functional group, and atleast one lanthanide metal-containing oxidant.
 2. The spin-onformulation of claim 1 wherein said water soluble polymer containingsaid at least one acidic functional group is selected from polyacrylicacid, polymethacrylic acid, polymaleic acid, polystyrene sulfonic acid,polytetraflourostyrenesulfonic acid, poly(ethylene-maleic) acid andpolystyrene carboxylic acid.
 3. The spin-on formulation of claim 1wherein said at least one lanthanide metal-containing oxidant includescerium as a lanthanide metal.
 4. The spin-on formulation of claim 1wherein said water soluble polymer containing said at least one acidicfunctional group is polystyrene sulfonic acid and said at least onelanthanide metal-containing oxidant is cerium ammonium nitrate.
 5. Thespin-on formulation of claim 1 wherein said aqueous solution comprisesfrom 5 weight % to 50 weight % of said water soluble polymer containingsaid at least one acidic functional group, from 5 weight % to 50 weight% of said at least one lanthanide metal-containing oxidant and theremaining water.
 6. The spin-on formulation of claim 1 wherein saidaqueous solution comprises from 10 weight % to 35 weight % of said watersoluble polymer containing said at least one acidic functional group,from 15 weight % to 25 weight % of said at least one lanthanidemetal-containing oxidant and the remaining water.
 7. The spin-onformulation of claim 1 wherein said lanthanide metal-containing oxidantis selected from a lanthanide metal nitrate, a lanthanide metalchlorate, a lanthanide metal perchlorate, a lanthanide metal bromate, alanthanide metal perbromate, a lanthanide metal permanganate, alanthanide metal chromate and a lanthanide metal dichromate.
 8. Thespin-on formulation of claim 1 wherein said at least one acidicfunctional group comprises a carboxylic acid functional group.
 9. Thespin-on formulation of claim 1 wherein said at least one acidicfunctional group comprises a sulfonic acid functional group.
 10. Aspin-on formulation comprising an aqueous solution of a water solublepolymer containing at least one acidic functional group, and at leastone cerium-containing oxidant.
 11. The spin-on formulation of claim 10wherein said water soluble polymer containing said at least one acidicfunctional group is polystyrene sulfonic acid and said at least onecerium-containing oxidant is cerium ammonium nitrate.
 12. The spin-onformulation of claim 10 wherein said aqueous solution comprises from 5weight % to 50 weight % of said water soluble polymer containing said atleast one acidic functional group, from 5 weight % to 50 weight % ofsaid at least one cerium-containing oxidant and the remaining water. 13.The spin-on formulation of claim 10 wherein said aqueous solutioncomprises from 10 weight % to 35 weight % of said water soluble polymercontaining said at least one acidic functional group, from 15 weight %to 25 weight % of said at least one cerium-containing oxidant and theremaining water.
 14. The spin-on formulation of claim 10 wherein saidleast one cerium-containing oxidant is selected from cerium nitrate,cerium chlorate, a lanthanide metal perchlorate, cerium bromate, ceriumperbromate, cerium permanganate, cerium chromate and cerium dichromate.15. The spin-on formulation of claim 10 wherein said at least one acidicfunctional group comprises a carboxylic acid functional group.
 16. Thespin-on formulation of claim 10 wherein said at least one acidicfunctional group comprises a sulfonic acid functional group.
 17. Aspin-on formulation comprising an aqueous solution from 10 weight % to35 weight % of polystyrene sulfonic acid, from 15 weight % to 25 weight% of cerium ammonium nitrate and water.